With Robert Downey Jr.'s contract renegotiations off to a start (not to mention every other Avenger as well... yikes!), a lot of talk is being made of just how integral Downey is to the Marvel franchise. To be honest, you're not going to get any argument about that here. Downey's commitment to the role, natural charisma, and superb acting chops all coalesced in 2008 to form the biggest surprise hero hit ever. Thanks to "Iron Man," the armored Avenger rocketed from Marvel's B-list all the way to the top. The guy is irreplaceable.

But is he the most successful superhero actor ever? To find out, I spent a lot of time on Box Office Mojo pulling data and making spreadsheets. I compiled a list of the top 10 most successful superhero actors, based on box office totals. There were a few requirements though:

» Actor has to have appeared in more than one film playing the same character

» Actor must have headlined at least one of those films

» Box office totals for films in which they made a cameo appearance were not included

So with all those rules out of the way, just how much is Robert Downey Jr. worth to Marvel and Disney?

So yeah, RDJ has plenty of reason to renegotiate, and Marvel has plenty of reason to keep him on board. Unlike Spider-Man and Batman (the only other characters in this list's Billion Dollar Club), Iron Man had never been prominent in pop culture before his 2008 film. One could make the argument that Spider-Man and Batman are so well-known that their success wasn't as dependent on the actors playing them (not to knock Tobey or Christian's phenomenal performances). But how did an unknown character like Iron Man become such a sensation? A lot of that is due to Downey.

Downey's lead over Tobey Maguire will continue to grow as "Iron Man 3" continues to rake in the dollars. The other people to watch, though, are Hugh Jackman and Chris Hemsworth. Unless something catastrophic happens to "The Wolverine," he'll be joining the Billion Dollar Club in a few months. And if "Thor: The Dark World" is a hit, then Hemsworth could crack the top five.

Are you surprised that Robert Downey Jr. is the most bankable superhero actor? Let us know in the comments below or hit us up on Twitter!